1. Field of the Invention
The present invention relates to a signal converting circuit and method thereof, and more particularly to an active balun circuit for signal transformation between differential and single-end and a method thereof.
2. Description of the Prior Art
A balun (Balance-unbalance) circuit is a transformer for transforming a single-end signal to a differential signal or transforming a differential signal to a single-end signal. Please refer to FIG. 1. FIG. 1 is a diagram illustrating a conventional balun circuit 10. The conventional balun circuit 10 is a passive balun circuit fabricated in two coils 11, 12 for transforming differential signals Vin+, Vin− to a single-end signal Vout. The differential signals Vin+, Vin− are applied to both ends of the primary coil 11 and the signal-end signal Vout is outputted from the first terminal of the secondary coil 12, wherein the second terminal of the secondary coil 12 is connected to a ground voltage.
Since the conventional balun circuit 10 is fabricated by two conducting coils, which is too bulky and difficult to implement into an integrated circuit. As for conventional active balun circuit, the poor 2nd order linearity limits its applications. Therefore, how to provide a high linear, especially low 2nd order distortion and low cost balun circuit for an electronic device is a significant concern in the field.